This invention is concerned with a disc brake system, for example for a wheel of a vehicle.
A conventional disc brake system comprises a hub mounted on a suspension link for rotation relative thereto, the hub providing a mounting for a wheel, and a disc brake comprising a disc mounted for rotation as a unit with the hub, friction material pads arranged on opposite sides of the disc, and at least one piston and cylinder assembly operable to urge the pads into engagement with the disc, to brake the hub and hence the wheel. Conventionally, the piston and cylinder assembly is slidably mounted on a slide bolted to the suspension link of the vehicle. The disc is conventionally rigidly fixed to the hub, and wear of the pads and/or the disc is accommodated by the sliding movement of the cylinder.
Disc brake systems are known in which the disc rotates with the hub as a unit but can perform sliding movement on the hub. For example, see GB 1 396 503 and WO 98/25804. However, since the discs are relatively thin, they tend to tilt on the hub and affect the braking ability. Also, there is a tendency for noise to be produced by rattle of the disc against the hub. At higher disc temperatures, these problems can be particularly severe since, when there is a large temperature differential, such as 600xc2x0 C., between the braking surface of the disc and the hub, the disc expands considerably, away from the hub, exacerbating the problems of tilting and rattle. These problems are addressed in WO 98/26192 in which the solution proposed is to provide a plurality of resilient force applicators which are mounted between the hub and the disc, the force applicators acting to apply radially-directed forces to the disc to control the movement thereof, the force applicators being distributed circumferentially around the hub. In the example given in WO 98/26192, the disc take system comprises two discs mounted on the same hub. One mounting means for the disc on the hub disclosed, in WO 98/26192 comprises groups of axially-extending grooves formed in the hub and teeth projecting from the discs into said grooves, the teeth being slidable along the grooves. The force applicators are in the form of leaf springs mounted on the hub in the spaces between the groups of grooves. This system requires that, at least between the groups of grooves, there is sufficient clearance between the hub and the discs to accommodate the leaf springs and flexing thereof. This clearance has the disadvantage that it increases the possibility that a disc may tilt relative to the hub, thereby adversely affecting the operation of the brake.
It is an object of the present invention to provide a disc brake system in which the afore-mentioned disadvantage is overcome or at least reduced.
The invention provides a disc brake system comprising a disc, and a hub which is arranged to rotate about an axis thereof, the system also comprising mounting means by which the disc is mounted on the hub so that the hub and the disc rotate as a unit about said axis and the disc can perform axial sliding movement on said hub, said mounting means comprising a plurality of axially-extending grooves formed in the hub and teeth projecting from the disc into said grooves, each tooth being a sliding fit in one of said grooves, the system also comprising resilient means acting to apply radial force between the disc and the hub, characterised in that said resilient means is provided by springs located in at least some of said grooves and engaging the teeth of the disc which project into those grooves to apply radial force to said teeth.
In a disc brake system according to the invention, the springs are accommodated in the grooves in the hub so that space for them does not have to be provided between the grooves enabling the clearance to be reduced substantially. This enables the possibility of the disc tilting on the hub to be reduced.
A disc brake system according to the invention may be as disclosed in WO 98/25804, except that the splined mounting means by which discs are mounted on a hub is replaced by mounting means as disclosed herein. The brake system of WO 98/25804 comprises one or more discs which are slidable on a hub under the control of leaf springs which act between the hub and the discs. The system also comprises a cylinder which is integrally formed with a suspension link and a caliper also fixed to the suspension link, the caliper having supports for friction material pads mounted thereon.
In a disc brake system according to the invention, the springs may be flat leaf springs as disclosed in WO 98/26192 or any other suitable type of spring. For example, the springs may be leaf springs each of which comprises at least three abutments which project transversely of the spring and engage the disc so that the abutments apply force to the disc. This arrangement has the advantage that the number of points of contact between the spring and the disc is increased thereby spreading the forces more evenly around the disc. The abutments may be provided by embossed portions of the spring. The abutments, preferably, are elongated so that each abutment remains in engagement with the disc throughout said movement of the disc on the hub. For example, said abutments may be in the form of ridges extending parallel to the axis about which the hub rotates. The leaf springs may be secured to the outer surface of the hub in a manner such that the springs extend tangentially on the hub when the disc is not mounted on the hub. Cut-outs, the holes, may be formed in the leaf springs to control the force applied by the abutments to the disc. Where the disc brake system comprises one or more further discs mounted on the hub, the leaf springs may be arranged in groups, the spring in each group being associated with each disc, at least one spring in each group being retained in position by a connection to another spring in said group.